1. Field of the Invention
This invention relates to a particle beam processing apparatus. In particular, this invention relates to a particle beam processing apparatus including a particle generating assembly, a foil support assembly having a thin foil, and a processing zone to cause a chemical reaction on a substrate or a coating.
2. Description of the Related Art
A particle beam processing device is commonly used to expose a substrate or coating to highly accelerated particle beams, such as an electron beam (EB), to cause a chemical reaction on the substrate or coating.
An electron is a negatively charged particle found in all matter. Electrons revolve around the nucleus of an atom much like planets revolve around the sun. By sharing electrons, two or more atoms bind together to form molecules. In EB processing, electron beams are used to modify the molecular structure of a wide variety of products and materials. For example, electrons can be used to alter specially designed liquid coatings, inks and adhesives. During EB processing, electrons break bonds and form charged particles and free radicals. These radicals then combine to form large molecules. By this process, the liquid is transformed into a solid. This process is known as polymerization.
Liquid coatings treated with EB processing may include printing inks, varnishes, silicone release coatings, primer coatings, pressure sensitive adhesives, barrier coatings and laminating adhesives. EB processing may also be used to alter and enhance the physical characteristics of solid materials such as paper, plastic films and non-woven textile substrates, all specially designed to react to EB treatment.
A particle beam processing device generally includes three zones. They are a vacuum chamber zone where particle beam is generated, a particle accelerator zone, and a processing zone. In the vacuum chamber, tungsten filament is heated to about 2400K, which is the electron emission temperature of tungsten, to create a cloud of electrons. A positive voltage differential is then applied to the vacuum chamber to extract and simultaneously accelerate these electrons. Thereafter the electrons pass through a thin foil and enter the processing zone. The thin foil functions as a barrier between the vacuum chamber and the processing zone. Accelerated electrons exit the vacuum chamber through the thin foil and enter the processing zone at atmospheric conditions.
Electron beam processing devices that are commercially available at the present time generally operate at a minimum voltage of 125 kVolts. These existing EB units utilize thin foil made of titanium having a thickness of 12.5 micrometers, to cure coatings on substrates that are being fed through the processing devices at a rate of 800-1000 feet per minute. For example, such an EB unit may be purchased from Energy Sciences, Inc. of Wilmington, Massachusetts, Model No. 125/105/1200. However, these processing devices do not function efficiently because most of the energy from the 125 kVolts is wasted. In addition, the current technology cannot be used in certain industries like flexible food packaging. An EB unit operating at 125 kVolts deposits substantial amounts of the energy onto the polyethylene based sealant films which contact the food being packaged. This deposit causes off-odors in the films and increases its seal initiation temperatures.
One way to increase the efficiency is by reducing the operating voltage below 125 kVolts. In addition, operating below 125 kVolts allows better control of the depth of energy deposition and minimizes the electron energy absorbed by the sealant films. However, when the voltage is reduced below 125 kVolts, the kinetic energy of the electrons traveling through the titanium foil decreases because more energy is being absorbed by the titanium foil, causing the foil to heat up excessively. Excessive heat causes the titanium foil to become blue, brittle, and lose its mechanical strength. Excessive heat also poses a problem with heat management of the system. Consequently, the feed rate of the substrate must be substantially reduced which makes the processing device commercially unviable.
In light of the foregoing, there is a need for a particle beam processing device that operates more efficiently, is smaller in size, has a reduced power demand, and is cheaper to construct.
The advantages and purposes of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The advantages and purposes of the invention will be realized and attained by the elements and combinations particularly pointed out in the appended claims.
To attain the advantages and in accordance with the purposes of the invention, as embodied and broadly described herein, one aspect of the invention is directed to a particle beam processing device that is smaller in size and more efficient. In accordance with the invention, the particle beam processing device comprises a power supply, a particle generating assembly, a foil support assembly, and a processing assembly. The particle generating assembly is located in an evacuated vessel and is connected to the power supply. The particle generating assembly operates at a first voltage in a range of 110 kVolts or less. The particle generating assembly includes at least one filament for generating a plurality of particles upon heating. The foil support assembly operates at a second voltage, which is higher than the first voltage, to permit at least a portion of the particles to travel from the first to the second voltage and exit the foil support assembly. The foil support assembly includes a thin foil made titanium or alloys thereof having a thickness of 10 micrometers or less. The processing assembly is for receiving the particles exiting the foil support assembly. The particles cause the chemical reaction on the substrate.
A second aspect of the invention is also directed to a particle beam processing device. Similar to the first aspect, the particle beam processing device comprises a power supply, a particle generating assembly, a foil support assembly, and a processing assembly, except that the foil support assembly includes a thin foil made aluminum or alloys thereof having a thickness of 20 micrometers or less.
A third aspect of the invention is directed to a method for causing a chemical reaction on a substrate in a particle beam processing device. The method comprises several steps including creating a vacuum in a particle generating assembly which has at least one filament, heating the filament(s) to create a plurality of particles, operating the particle generating assembly at a first voltage having a range of 110 kVolts or less, operating a foil support assembly having a thin foil at a second voltage, which is higher than the first voltage, to cause at least a portion of the particles to travel from the first voltage to the second voltage, and to exit the vacuum in the particle generating assembly, the thin foil being made of titanium or alloys thereof and having a thickness of 10 micrometers or less, and passing the exiting particles through the thin foil to enter a processing assembly where the substrate is being exposed to the particles.
A fourth aspect of the invention is also directed to a method for causing a chemical reaction on a substrate in a particle beam processing device. Similar to the third aspect, the method comprises the same steps except that the thin foil is made of aluminum or alloys thereof and having a thickness of 20 micrometers or less.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as claimed. Additional advantages will be set forth in the description that follows, and in part will be understood from the description, or may be learned by practice of the invention. The advantages and purposes may be obtained by means of the combinations set forth in the attached claims.